1. Technical Field
The disclosed embodiments relate in general to a display apparatus with a symmetric diffusion film, and more particularly to a display apparatus with a touch sensor and a symmetric diffusion film, which uniform the luminance distribution.
2. Description of the Related Art
Touchscreens are becoming widely used in electronic products, such as handheld devices (cell phone, PDA, . . . etc.), or tablet computers, to serve as input devices for the user. A touchscreen is an electronic display with a touch sensor able to detect the presence and location of a touch within the touch-sensitive area or the display area. The touch on the panel can be executed by a finger, a hand, or an object such as a stylus.
The four most common touch sensor technologies include resistive, infrared, capacitive and SAW (surface acoustic wave). Each technology offers its own unique advantages and disadvantages. Resistive and capacitive touch sensor technologies are the most popular for industrial applications due to their good reliability. The capacitive type touch sensor has advantages of a small touch force and can support multi-touch detection, while the resistive type touch sensor cannot determine where multiple points on a resistive type touch sensor be touched. However, the cost of a capacitive type touch sensor is high because of several photolithographic steps required in a manufacturing process, and the method for detecting and determining the locations of multiple touched points on a capacitive type touch sensor is complicated.
For touchscreens, the methods for integrating a touch sensor to a display panel include three different types of In-Cell touch, On-Cell touch, and Out-Cell touch. An In-Cell touch sensor is physically inside a display (ex:LCD) cell and the touch sensor can be light-sensing elements (light-sensing), micro-switches (voltage-sensing) and capacitive electrodes (charge-sensing). An On-Cell touch sensor is developed on a color filter substrate, for example, an X-Y array of conductors (ex: ITO or metal) on the top or bottom surface of the color filter substrate. An Out-Cell touch sensor is laminated directly on top of a display (ex:LCD) cell during manufacture.
Take In-Cell and On-Cell integrations for example, which one or more layers of sensing electrodes of touch sensor can be developed on a color filter substrate. FIG. 1 schematically illustrates a conventional touchscreen having a touch sensor integrated to a display panel. As shown in FIG. 1, a display panel typically includes a TFT glass substrate 11, a CF glass substrate 13, a liquid crystal (LC) layer disposed between the TFT glass substrate 11 and the CF glass substrate 13, and a backlight system 17 under the TFT glass substrate 11 for emitting the light forwardly. A black matrix layer 133 (ex: about 6 μm in width) can be further formed on the inner side of the CF glass substrate 13. The touchscreen of FIG. 1 comprises the touch sensor such as the sensing electrodes 19 (ex: metal electrodes, with a width smaller than 6 μm) positioned on the top of the CF glass substrate 13 and corresponding to the black matrix layer 133. Due to parallax effect in the thickness (such as 0.2 mm) of the CF glass substrate 13 and light-blocking by the sensing electrodes 19, luminance distribution mura occurs while the touchscreen is viewed at the side angle (off-axis).
FIG. 2 is a simulation result showing luminance distributions of the conventional touchscreen (a display panel with a touch sensor) of FIG. 1 and a display panel. For the display panel (without touch sensor), the luminance distributions is a smooth curve, exhibiting decrease of the luminance with increase of viewing angle (Theta; angle to normal-axis). Although the luminance distributions of the conventional touchscreen of FIG. 1 shows the similar tendency as the display panel (without touch sensor), it is an uneven curve because of interference of sensing electrodes 19 and the black matrix layer 133 in display; therefore, luminance distribution mura will be visually observed during off-axis viewing.